Diamond is an exceptionally useful functional material due to its rare combination of unique physical and chemical properties. Among them are the highest hardness, highest thermal conductivity, high Young's modulus, outstanding chemical inertness, semiconducting wide band gap property, and negative electron affinity which profit its use in both mechanical and electronic applications including field emitting devices [J. E. Field “The properties of natural and synthetic diamond” Academic Press; London, 1992]. Diamond can be synthesized in bulk crystalline forms using a high-pressure and high-temperature method and in film forms employing chemical vapor deposition (CVD) in most cases based on hydrogen environment (including plasma) with a carbon precursor [S. Matsumoto, et al., J. Mat. Sci., vol. 17, pps. 3106-3112, “Growth of Diamond particles from methane-hydrogen gas”, 1982]. Highly oriented diamond films have been available and prepared on various substrates using bias-enhanced nucleation (BEN) on mirror-polished substrates [S. Yugo, et al., Appl. Phys. Lett., vol. 58, pps. 1036-1038, “Generation of diamond nuclei by electric-field in plasma chemical vapor-deposition”, 1991] or by controlling the growth parameters on pre-scratched substrates [C. WILD, et al., Diamond Relat. Mater., vol. 3, pps. 373-381, “Oriented CVD diamond films—Twin Formation, Structure and Morphology”, 1994].
Diamond is of great interest in many experimental methods of analysis and testing such as, for example, scanning probe microscopy (SPM), nanoindentation and other nanoprobe techniques. The extreme hardness, the high Young's modulus, the inherent chemical inertness, and the electrical conductivity obtained through doping make this material particularly attractive. Due to the unavailability of sharp single crystal diamond tips on a nanoscale range, some probing tips of atomic force microscopes (AFM) are constructed from silicon coated by diamond. Such technology enables the preparation of tips with radii of 100 to 200 nm [P. Niedermann, et al., J. Vac. Sci. Technol. A, vol. 14, pps. 1233-1236, “Chemical vapor deposition diamond for tips in nanoprobe experiments”, 1996; T. Trenkler, et al. J. Vac. Sci. Technol. B, vol. 18, pps. 418-427, “Evaluating probes for “electrical” atomic force microscopy”.] for the best and uneven diamond surfaces.
Such tips with high aspect ratio may have an advantage in improving the image resolution. The large radii of the tips may, however, induce distorted images in some topographical surface environments. In addition, because of the high aspect ratio of silicon tips and silicon properties, such diamond coated silicon tips are easily broken during accidental contact with the surface or during scanning the tip over a surface.
Diamond tips are also made by a so-called moulding technique employing the fabrication of pyramidal pits in silicon by anisotropic etching and subsequently filling them by CVD diamond. The chemical removal of silicon then yields diamond pyramids as small as 20-50 nm [P. Niedermann, et al., Appl. Phys. A, vol. 66: pps. S31-S34, “CVD diamond probes for nanotechnology”, 1998]. However, the pyramids are polycrystalline diamond and have a low aspect ratio. During manufacture, the pyramidal pits produced in silicon are often not filled by polycrystalline diamond completely and therefore diamond grains are frequently missing on the tip apexes. Thus, diamond tips, which are made of single crystal diamond with high aspect ratio, smaller tip radius and defined crystal orientation would have intrinsic advantages over polycrystalline diamond pyramidal tips being used in AFM probe applications.
Since diamond has negative electron affinity, there is a potential application of diamond in field emitting devices as discussed by Wei et al [W. F. Wei, et al., Carbon, vol. 13, pps. 425-427, “Photoelectric emission and work function of semiconducting diamond” 1975]. However, the high switch-on electric field of normal CVD diamond has limited diamond in such applications. The formation of high-density sharp tips of diamond would certainly decrease the switch-on electric field and promote its field emission applications. A notable application of high-density diamond tips would be a substitute for the filament emiiter in cathode ray tubes widely used in televisions.